For future reference (yes, I see that the question was answered, but future searchers will benefit):

1. There are luggage lockers and Smarte Cartes available in Chicago Union Station's baggage claim room, which is also typically staffed. In most cases, people should (as mentioned above) just check their luggage through.

2. The luggage area is below the passenger concourses, and access to that floor is restricted to employees. If you're retrieving or checking a parcel, you have to ask an employee to walk you over.